1. Field of the Invention
The present invention relates to a disc drive control method and apparatus, and more particularly, to a method and apparatus to compensate for a difference between an actual torque constant and a modeling torque constant used for servo design in a disc drive.
2. Description of the Related Art
Japanese Patent Publication No. 2002-367307 discloses a device detecting a current and a voltage using a voice coil motor (VCM) current detector and a VCM inter-terminal voltage detector, calculating a coil resistance value and a torque constant, and correcting a seek loop gain based on the coil resistance value and the torque constant.
A data storage device, i.e., a hard disc drive contributes to a computer system operation by reproducing data from a disc using a magnetic head and recording data onto the disc. With high capacity, high density, and a compact structure of a hard disc drive, a bit per inch (BPI) indicating a density in a rotating direction of a disc and a track per inch (TPI) indicating a density in a radial direction thereof have been increased. As a result, a fine mechanism is desired.
A hard disc drive includes a plurality of magnetic transducers that read and/or write information by sensing a magnetic field of one or more rotating discs and/or magnetizing the one or more discs. Information is stored in a plurality of sectors positioned within an annular track. Track numbers are positioned across a surface of a disc. Numbers owned by vertically similar tracks are referred to as cylinder numbers. Accordingly, each track may be defined by a cylinder number.
Each transducer is typically integrated within a slider included in a head gimbal assembly (HGA). The HGA is attached to an actuator arm, which has a voice coil positioned adjacent to a magnetic assembly. The voice coil and the magnetic assembly define a VCM. A hard disc drive typically includes a driving circuit, and a controller to supply current that excites the VCM. The VCM rotates the actuator arm and thus moves transducers across the surface of the disc.
When writing and/or reading information, the hard disc drive may perform a seek routine to move the transducers from one cylinder to another cylinder. During the seek routine, the VCM is excited by current and moves the transducers to a new cylinder position across the surface of the disc. The controller performs a servo routine to guarantee that the transducers are moved to an exact cylinder position and to a center of a given track.
It is preferable to minimize a time required to read information from and/or write information to a disc or discs. Accordingly, the seek routine performed by the hard disc drive should be implemented so that the transducers are moved to the new cylinder position within a short time. In addition, a time to stabilize the HGA should be minimized, so that the transducers quickly write and/or read information and are positioned adjacent to the new cylinder at one time.
Since a torque constant of the VCM of the hard disc drive changes depending upon a state of a head disc assembly and a component characteristic of the VCM, a modeling torque constant determined during servo design may be different from an actual torque constant appearing in the hard disc drive during operation. A big difference between the modeling torque constant and the actual torque constant affects servo performance, and therefore hinders fine seek servo and elongates seek time.